Various types of locating devices e.g. for underground cables, are known. One such device, produced by the applicants, detects a magnetic field produced by an electric current in an underground cable using a pair of detector coils. The device gives an indication of when the user is directly above a portion of the buried underground cable. Typically, the user then marks the position of the cable on the ground surface and then moves along the cable detecting further portions of it. Thus the position of the length of cable can be determined.
Once the position of the cable has been determined it is useful to record this for future reference. Traditionally this would be done by simply recording, for example, that the cable lies a certain distance from the edge of a road, or alternatively by marking the cable on a map using conventional map surveying techniques.
Such recordal methods give rise to the problem that, when the user returns at a later date to re-locate the cable, they may need to re-use complex surveying techniques to relate the information on the map to the actual location. There is also the possibility that the physical feature (such as, in the above example, the road) which references the location of the cable has been moved. These problems render the repeatability of locating the cable more difficult, and furthermore involve the use of skilled techniques.
The present invention aims to reduce the complexity of recording the location of an underground object, such as a cable, and to increase the ease with which the object can be re-located.